Signaling system



Nov. 20, 1928.

J. F. FARRINGTN S IGNALING SYSTEM Filed March 11, 1924 `Patented Nov. 20,1928.

UNITED STATES 1,692,437 :PATENT OFFICE.

JOHN E. FAERINGTON, or vELUsHnve7 NEWYOEK, Assrenon 'ro lWESTERN ELEo'rEIc comun, INCORPORATED, or New Yoan, n. Y., A conronarron OENEW YORK.

SIGNAniNG SYSTEM.l

y Application filed March 11, 1924 Serial N'0.'G^98,358.

This invention relates toV signaling systems and, as illustrated in the embodiment herein described, is particularly adapted for use in radio telephone systems.

An object of the invention is to provide imroved methods kof and means yfor two-way iigh frequency., particularly' radio, signaling, whereby reception may be accomplished eliiciently and without harmful interference l either from Waves simultaneously tra-nsmitted from the outgoing transmission channel of the same two way system, from incoming or outgoing transmission of otherk twoway systems that might be combined with it i5 to constitutev a multiplex system, or from other transmissions not related to the system under consideration simultaneously traversing the same transferring mediunnforexample, the ether.

In a well-known type'of carrier wave signal system disclosed, for example, inFrench Patf ent 24,792, patented June 26, l922,.constituting the first addition vof Patent 541,217, oppositely directed transmissions of a two way if signaling channel utilize continuously transmitted carrier waves differing in frequency by an amount above that used for modulation Y in either direction. Provision is made whereby the receiver at each stati'onreceives carfl rier wave from its own transmitter, as well'as from the distant station.` These two different frequency waves, either or both ofvwhich y y' may be modulated, are combinedat either station to produce another carrier wave called :i5 the auxiliary carrier wave, which is modulated in accordance with the modulations of the carrier waves concerned in its production.

This modulated auxiliary carrier wave is detected toproduce the signal, or signals. This 4o type of system has the beneficial attributes of the well-'known heterodyne system, whichit in many respects resembles, namely, it provides an efficient means for signalamplification (either in the first detector itself" or in separate auxiliary frequency amplifiers). 'It has the further unique advantage that the side toneinterference from the transmission may be strictly limited. For example, if the r`same percentage of modulation 'is used for both systems of transmission., the reproduced normally received signals and the interfering side tone signals have equal intensities regardless of the relative quantities of energy associated with their respective carrier currents..

Accordingly, an adjustment to produce a dein suc-h places. Y

sired amplitude of incoming signal which is possible of attainment for widely different conditions of interlinkage of the transmitting and receiving circuits) insures that theside tone will be within permissiblelimits.

The

practical necessity on ship board and ink similarly restricted areas Vofusing closely contiguous 'transmitting and receiving antennae,

-or a common antenna, where excessive' side tone would otherwise negative the eiicient use of thecircuits, has, for the above reason, favored the use of'this type Of two way system In another equally temnot necessarilyy limited to twoway operation, the production of the signal modulated carrier wave is accompanied, or followed, by suppression of the unmodulated carrier with well-known ktype of sysi l attendant advantages, among rV others, :of

energy conservation and comparative secrecy. The i,practical embodiment of such a carrier suppression system in a two way. system of the type described above, presents difficulties, since the product of the first'stage of detection f therein would not include awave ofthe uni modulated auxiliary carrier frequency, which is necessary for the reproduction of the `signal lin the subsequent stage. of detection.

It is a further object of this inventionto provide improved means for overcoming 'thatdi'liiculty, that is, to provid-e atwo-way'fsystem having` all of the important features of thev two-way system described, and which has they additional advantages inherent in any system operating on the suppressed carrier principle. In the system, according to one mode of operation, arminute amount of the unmodulated carrier is transmitted. This amount is insignificant so far as it affects the amount of energy concerned in transmission. Itis insuilicient to permit the reproduction of the signal by simple detection.v It'is insufficient even for signal reproduction by double detection in accordance with conventional methods of operating two-way systems of the general'l type described. In the method of receiving such a wave practiced by this. invention, energy from the transmitting circuitat the,y same station, amplified if necessary, is impressed on the first detector through Aa separate conductive connection. The invention, as to this feature, differs from that of applicants U. S. Patent 1,495,470, May 27, 1924, in that the circuit for conducting this energy is tapped into-the, transmitting circuit at a `carrier is suppressed and without regard to t-he particular means for obtaining the reinforcing wave at the input of the first detector.' lt functions, in any form of such system, to give greater security from pulses, or similar phenomena origina-ting in the transmission circuit or elsewhere, than can be secured by the use of resonant circuits. lts

highly selective qualities enable it to discriminate from undesired carrier waves which are incident on vthe antenna. ltris also useful in a system where it would otherwise be difficult tolimit'the amount of energy transmitted from vthe antenna. to the receiving circuit to. asufticiently small amount for efficient reception by the auxiliary frequency method. Y

A feature of the invention which imay, in special cases, be used with or without the cooperation of the filter to completely prevent, or to regulate, the flow of current fromy the transmitting to the .receiving circuit,where a common antenna is used, is the connection of the transmitting'circuit to the antenna in balanced relation with respect to the points to which the receiving circuit is connected. (0

of the unmodulated carrier may be used at `both stations, if separate local sources are Complete, instead of apartial suppression used with each stage of demodulation If the distant station transmits some unmodulated carrier, ofcourse the product ofthe first demodulated operation would contain an unvos modulated auxiliary carrier wave, so that in this case, a local source, otherwise used with the second stage of demodulation, would be unnecessary. Y

The inventionincludes a novel means for producing a modulated wave characterized ,by complete or any desired degree of partial suppression of the unmodulated carrier com,

ponent.- Two carrier wave oscillators are vcoupled together in balanced relation so as normally to `produce no output wave. The modulating wave is differentially impressed upon the space current paths of the balanced oscillators to proportionally'imbalance the circuit, as in the quite similar balanced modulator circuit. Y i

` A particular advantage in the use of suppressed carriertransmissioninheres in the operation of two-way circuits on board ship The effect on the receiver output of transient oscillations produced by sparking during the transmitting intervals when power is on the antenna may be reduced by the use of an efficient high :frequency filter (in the po sition BF of the diagram) designed to reduce the potentials impressed on the input of the receiving set from the transmitter of the saine station s to the desired minimum consistent with its function of transmitting the carrier frequencies. from the transmitters of both stations to the high frequency detector where they are inter-modulated to produce the aux-- iliary carrier wave.

Furtlieicbjects and features will be apparent to those skilled in theart from a reading of the following detailed description with reference to the accomp aiiying drawing which represents a station of a two way system having the features of, and capable of opera-tion according to, the inver tion.

In the drawing a common antenna lill is used both for transmitting and receiving.

The elements l, SA, QM d l3nt atthe left of the antenna are respectively, `a signal frequency source, a signal current amplifier, an oscillator-modulator and avpower ampli. ier.

They cooperate to produce a signal modulated wave having all or any desired part of its unmodulated carrier wave suppressed. Through the medium of suitable tilters in the input amplifier PA, either side band of the moda lated wave may be suppressed if desired. For convenience, the system will be `assumed to be used for speech signaling.

A'lhe elements, BF, DM, BR, DM,bv LF and 2, at the right of the antennaware res; cctively, a high frequency band pass filter, a. high frequency dcmodulator, an aiiiriliary frequencyiband pass filter, an auxiliary frequency demodulator, a low pass hlter and an indicator. They cooperate with each other and with the transmittingl circuit in the inanner to be described to receive speech :nodulated waves transmitted from-a distant sta tion and to reproduce therefrom a modulating component. The carrier frequencies for ion p transmission and reception differ by an,A

amount above audibility.

Depending upon the particular adjust ments of the several elements, and in some instances, on the choice of elements used,

the system as a whole and its contained elements are capable of Widel different functions. The elements will rst be described without special reference to `their respective possible functions'in the system'as awhole and this will be followed by a description of the operation ofthe system.

The oscillator-modulator'OM is similar to oscillator-modulators generally in that it includes means whereby the current from the signal frequency source l, after amplification in signal or speech amplifier SA, is employed to vary'the condition of oscillation of acarrier wave oscillator to the extent that its variations are impressed on the resultant high frequency current-ofthe oscillator.

It differs from conventional oscillatormodulator circuits in that the oscillator when not subjected to signal modulation, delivers no carrier wave to its output circuit. Electrical discharge devices 3' and 4 with their associated circuits -each constitute a, feed back oscillator of the well-known tuned input type. The input circuit of oscillator 8 is constituted by circuit 5, 6 containing the frequency determining resonant circuit 7, the grid leak resistance 8 and thegrid condenser 9. The input circuit is coupled with the output circuit, which includes conductor 10, conductor 11, coupling coil 12, and transformer primary 13. The circuit of oscillator 4 is similar and includes in common there- I with'the elements 5 rand 7 to 12 inclusive. The input and output circuits are completed through paths `distinct, from those used by oscillator 3 including respectively, conductor 14 and transformer primary k15. Since the oscillators have a common frequency den termining circuit theyk oscillate at the same frequency.` However, the transformer primaries 13 and 1'5 are wound in the same direction, considered as portions of a single winding, and are traversed by currents in respectively opposite directions, vso that if the output currents are in the same phase within the Acommon portion of, their circuits, and'of equal value` their effects in the seconda'ries 16 and 17 are balanced, assuming that the individual transformer constituted respective- -ly by windings 13, 16 and 15, 17 have equal ratios of turns. tion of the currents in secondari-es 16' and 17 is insured by the arrangement of the respective input circuits whereby the input energy is impressed from coupling coil 12 and transslated to the respective input elements in the same phase. The relation of input and output currents is perpetuated by constituting coupling coil 12, a portion of la circuit which is common to the two output circuits.

Space current for the two oscillator tubes is .supplied by source 18, which also supplies the space current for amplifier SA. through circuitsQO and .21 respcctivelv. Condenser 19 by-passes the generated high frequency The desired balanced rela-`A currents around this battery. By preliminary adjustment the output circuits may be made balanced or not, as desired. If balanced, the oscillator normally produces no carrier wave in the output circuit y16, r17; ify unbalanced, a wave whose amplitude is proportional to the degree of unbalance. If the space current circuit of one of the oscillator units is interrupted the other units function in a conventional manner as a single tube` if the circuits are initially adjusted to Vgive a *A perfect balance of generated currents, modulation results in an imbalance proportional to the impressed modulating Vcurrent and consequently, the production of a resultant wave whose amplitud-e and frequency vary in accordance with the modulating current. The output accordingly includessignal modulated side bands without any unmodulated carrier.

The modulation product is ampliiied by power amplifier 13A-and impressed on kantenna AN.

Elements inthe transmitting system'which have not been specifically mentioned are wellknown in the art and need no description. Modulation bythe `method of impressing 'modulating potentials on the plate of a modulatortube is old, and isv disclosed, for eX- ample, in British Patent 15,237 of 1915. j

The transmitted energy is impressed on the antenna 'circuit between ground anda point between the ends of inductance S24. The en- 'l so orgy accordingly flowsv between these two y points in parallel paths, one of which includes the aerial and its capacity to groundl and the other the artificialA network N which is designed to simulate theelectrical characteristics ofthe first iath. `A.ccordingly, with a particular critical j iositioning of Jthe yintermediate point a balance can be effectedpassing with negligible attenuation currents in a definite band of frequencies, suchas one or more incoming carrier side bands with or without some unmodulated carrier, and to substantially completely attenuate currents of all other frequencies. The type illustrated is disclosed in U. S. patent to Campbell 1,227 ,113, granted May 22, 1917. Depending upon the degree of perfection of the balance, or the degree of perfectionl of the filter in excluding currents of frequencies outside of its normal band, or upon both of these means, all or any desired amount of the energy from the transmitter may be excluded from the receiving circuit.

The signal modulated wave from the distant station which is passed through the filter together with carrier energy transmitted through the lilter from the transmitting cirv cuit or, in the alternative, transmitt-ed there- Y from through auxiliary circuit 26V including amplifier A, if necessary, or from a separate local source 27 is impressed on the high frequency demodulator DM. if both of the last two mentioned sources ofcarrier frequencies are provided, a proper choice therebetween then may be made by switch 28.

Demodulator DM is of the balanced type which is completely disclosed in U. S. patent to Carson 1,343,306, granted June 15, 1920. Any other type of demodulator using one or more tubes may equally'well be used. It is characteristic of thebalanced type that, if critically adjusted, the demodulated out-put contains no component having any of the frequencies of the currents impressed on the common path of the divided input circuits or any component resulting from the combination of these currents. Accordingly, if the reinforcing current is transmitted through the filter, the demodulator circuit must be unbalanced or the circuit of one tube made inoperative so as to effectively constitute the circuit a single ltube demodulator.

The resultant auxiliary carrier frequency, together with the side bands, are selected by band pass filter BFl, which may be similar to band pass filter BF, and combined in auxiliary frequency demodulator Dil/l1. This demodulator instead of being of the balanced type illustrated may be of any conventional type. if the incoming high frequency wave does not include an unmodulated carrier component, so that the high frequency demodulator does not yield an unmodulated auxiliary carrier wave, this wave may be supplied by local source 29.

The resultant signal component is selected Vand transmitted through low pass filter LF and indicated in telephone receiver 2.

The system Vmay be operated in accordance with various modes as follows:

Sparlring between metallic parts of a ship subjected to the influence of the strong outgoing power would result .in transient oscillations being produced by an otherwise unmodulated transmitted carrier. The effect of '27 which must produce a frequency which dif-V fers from the incoming carrier frequencies by an inaudible amount, but does not have to havea frequency identical with the outgoingv carrier frequency. A second local source 20 is used if the current issuppressed at the distant station. l A l Y y 1 If the carrier is not suppressed the effect in the receiver of noise modulation of the car-- rier can be reducedby means of the -filter- BF. Reinforcing current can be supplied by the local source 27. The choice as to the use of the second local source is the same as for the first mentioned case. i Y

The balanced connection of the transmitter to the antenna, with or without the filter, may be relied on to prevent disturbances originating in the transmitting circuit from affecting the receivingcircuit, a separate localsource fof reinforcing waves being used.` This arrangement can similarly be used whenever it is desired to prevent the transmittedv carrier currents, or this current modulated, from entering the receiving circuit. The modulator oscillator may be adjusted to give van insufficient unrnodulated carrier to yield a signal by simple demodulation. However,l reception -by the auxiliary frequency demodulation method provides an auxiliary frequency carrier which may be separated from its side bands, amplified, and combined` therewith in the second demodulator as disclosed in applicants U. S. Patent 1,495,470, May v27, 1924. Alternatively, sufficient. auxiliary current may be obtained by using the auxiliary circuit 26 and amplifier A1. Circuit26 is cons.

nected to the transmitting circuit in such manner as to impress a side tone on the receiving circuit during signal transmission from the saine station. A local source 27 can be used alternatively with circuit 20, as above explained, or the auxiliary circuit can be connected directly` to either oscillator 3 or 4, as in the similar arrangement described in U. S. Patent 1,495,470, May 27, 1924, above mentioned.

Obviously the auxiliary circuit 26 or the local sourceV (or sources) could be effectively used even if the uninodulated carrier is transmitted. 4F or example, conditions might require such a degree of selection by filter BF as to prevent thetransmission of sufficientreinforcing current therethrough. @n the -other hand, reinforcing current may be sup-k lill) lil plied from the transmitting circuit to the lreceiving `circuit* throughthev antenna by respectively unbalancing the connection a predetermined small amount or` byusing a .filter which will transmita sufiicient quantity -of current of the'transmitted carrierwave, rfrequency. Use `ofthebalanced connection in a similar circuit is disclosedl Vin Fig.l 5` ofr vFrenchlatent 24,7 92, patented'June 26,1922,

of high frequency -carrier ywaves for transmitting outgoing signals, means for combining waves from said source ywithwincoming waves whereby waves of an inaudible frequency different from that of either of said frequencies are produced, and means for deriving audibleA incoming signals from said last mentioned wave. f n

2. A radio station comprising means for producing a signal modulated carrier wave, common means for radiating said Wave and for receiving a signal modulated carrier Wave whose frequency differs by an inaudible amount from that of said first mentioned car- Y rier wave, means for deriving signals from said received Wave, a band pass filter selective at the frequency of the received wave between said common means and said signal deriving means, said signal `deriving means comprising means foi` combining energy ofthe outgoing wave with energy of the incoming Wave to produce an inaudible frequency signal modulated auxiliary carrier wave, and means for deriving incoming signals from saidv auxiliary carrier Wave.

3. A radio station vcomprising means for producing a signal modulated carrierwave, means for radiating said Wave and for receiving a signal modulated carrier Wave whose frequency differs by an inaudible amount from that of said radiated Wave, means for deriving signals from said received wave, a band pass filter selective to the received Wave between said receiving means and said deriving means, said deriving means comprising means for combining energy of the outgoing and incoming Waves to produce an inaudible frequency signal modulated auxiliary carrier Wave, and means for deriving incoming signals from said auxiliary carrier wave.

4. The method of signaling between two stations which comprises generating at each station a carrier wave, at intervals modulating said carrier wave in accordance with signals, continuously transmitting said carrier waves modulated at intervals, radiating aty least a portion of the transmitted wave at each station, receiving a wave incident on at r`least one station from the other station, re-

ceiving a portion of the transmitting wave f at the local station independently of the radiationV and ofthe first mentioned receiving step combining .said received wavesto produce an auxiliary carrier Wave modulated at intervals in accordance with the signal modulations at both stations, and reproducing a signal from said auxiliary carrier wave.

5. The method ofy secret signaling between two stations which `comprises continuously transmitting carrier waves from each station, at leastk part of the time transmitting.

from each station signal modulated 'side bands of said Waves, the unmodulated carrier component transmitted from at least one f station being too small to reproduce al su-flciently perfect signal by single detection,.;

selectively receiving. the waves incoming-Yon each station, combiningy the received modulated small-amplitude carrier Waves .with a wave derived from the signal modulated wave at the-same station to produce an auxiliary carrier wave modulated by the signal at both stations, and reproducing the signals from said auxiliary carrier wave.

, 6. A station ofa signaling system comprising a generator of carrier frequency waves, means for modulating said Waves in accordance with signals, means for radiating said modulated waves and for receiving incoming waves, a demodulator, a non-signaling circuit between tlie output circuit of said modulator and said demodulator, means for selecting a signal modulated combination component from the demodulat-or product, .and meansfor reproducing the signals from said modulated 'combination component.

7 A station of a signaling system comprising a source of carrier frequency Waves, means for modulating said waves in accordance with signals, a common means for radiating said modulated waves and for receiving `modulated incomingv waves, a demodulator, a band pass filter between said common means and said demodulator sharply selective to the incoming Waves, a non-signaling circuit between the output circuit ofk said modulator and said demodulator,ineans for selecting a signal modulated combination component from the demodulator product, and means for reproducing the signals lfrom said modulated combination product. 8. In a station for communication systems,

a grounded antenna comprising a radiating member an impedance member and an artificial network, a transmission `circuit connected between two points in said antenna,

one point being between the ends of saidrim.`

pedance, a receiving circuit associated with yai said antenna in such a manner as to derive'` impedance of the halancing'- network to--f gether being such that a minimum of energy from the transmitting circuit is impressed on said receiving circuit, a localsource having a frequency differing by an inaudible amountl from that ot' the received Waves, means :tor combining the received Waves With Waves from said source to produce a modu lated auxiliary carrier Wave, and means to reproduce a signal Vfrom said auxiliary carrier Wave.

9. A system for generatingI Aa modulated carrier Wave having substantially no un# modulated carrier component comprising a` pair of electric discharge devices each includring a filament, an anode and a control electrode, input circuits respectively connected to the filaments and control electrodes ot said device and including a lcommon portion, a' timed circuit in said portion, outputl circuits respectively connected to the `lilaments and anodesof said devices and eachfincluding a common portion and an individual portion, aV

feed back circuit lin the common .portion of the constants ofthe remaining parts of the mally oscillating condition of the system there is a resultant difference of potential across saidA Winding corresponding to a desired degree otunbalance, and means for im pressing modulating currents on the fanodes of said devices 'in relatively opposite phases.

ln Witness whereof, I' hereunto subscribe l my name this 4th day of March, AfD. 1924.

. JOHN F. iAnRiNGioN.-

- system being so determined that in the nor- 

